Cover

Build a Bat House

Photos and story by Carla Brown, NWF Web Producer

I love bats because mosquitoes LOVE to bite me. Pesticides can be harmful to mosquitoes’ predators as well as mosquitoes. According to Bat Conservation International, one little brown bat can eat 60 medium-sized moths or over 1000 mosquito-sized insects in one night!

Bats are also interesting because:

In many ecosystems, they play a key role in pollinating plants.

There are more than 1,300 species of bats in the world!

Some bats use echolocation, or high pitched chirps which bounce off objects in front of them, to find their way in the dark.

Before I share my bat house building experience, let me say that I am no carpenter. This was my first time using a circular saw. Hopefully this can help even the least handy person build a bat house.

Why Build a Bat House?

You might be surprised: bats don't always live in caves. Some bats spend winter months in caves, but most bats spend summers in trees, under bridges or in old buildings, where they give birth and rear young.

Your goal is to make a bat house that mimics the space between bark and a tree trunk. That would be the bats' ideal nursery. That's why the space inside a bat house is very narrow, unlike a bird house which would house a nest. Bats like tight spaces. They also need it nice and warm for the babies. That's why we paint the box a dark color in most climates and why we caulk the sides to keep the heat in. Also, you'll be using a saw to rough up inside the box. That makes it more like tree bark and easier for the bats to climb up.

You might wonder why you need to build a bat house. Why can't the bats just find a nice tree? That is the challenge for many bat species as forests are cleared. Ideally they would live in a natural home but we build bat houses to help those who can't find space in a forest.

How to Build a Bat House

First I printed the Small Economy Bat House plan (pdf) from Bat Conservation International's website. (They also have a Bat House Builder’s Handbook available for free in a digital version on their bat house pages.) The big surprise was that this bat house ended up being bigger than I expected: two feet wide and almost three feet tall! According to their website, a successful bat house can be smaller (14 inches wide instead of 24 inches wide), but this one was designed to easily use up a 2 foot by 4 foot piece of plywood with fewer cuts.

That was not how I had pictured a bat house. Have you ever seen bat houses for sale that are smaller or shaped like a bird house? I have. That just means those houses were made by people less acquainted with bat needs.

I read over the plan and I found that I needed a location with:

lots of sun;

at least 15 feet off the ground (to protect against predators); and

ideally a water source nearby (so the mother bat doesn't have to leave her young for too long).

Interestingly, bats are less attracted to bat houses mounted on trees. There's a few reasons for this:

It's too easy for predators to get bats as they exit

The branches causing obstructions to exiting bats which drop down then up into flight

It's too shady from branches above.

Bat houses mounted on buildings retain heat better and are less accessible to predators. You can put them on a pole though. Luckily my townhouse is three stories high and has a sunny side. It's also near a stream. So I felt I probably had a good site.

When you buy a piece of wood that is advertised as 1 inch by 2 inches, it is not actually that big when you measure it. It's more like 3/4 inch by 1 1/2 inches. That was important for me to know because it allowed me to use scrap wood for part of the project.

The supply list in the bat house plan was very helpful, but I would add:

Two clamps for clamping wood while you saw or drill

Safety glasses for when you use power tools

A small broom for sweeping sawdust

Also, the bat house plan calls for paint. I didn't know what color and initially I thought white to match my house trim. But then I checked their website and they have a map where you look up what color to paint your bat house. For my area, I need dark brown or gray.

Building the House

Step 1: Wood Cutting (30 minutes)

Measure and mark where you need to cut the wood according to the plan. Clamp it down to a sturdy spot for safety. You cannot safely hold the wood and the circular saw. Adjust the blade to the correct depth depending on the width of your wood. It takes only five cuts. Don't forget your safety glasses.

At this point, I took the wood and laid it together to get a sense of how this was going to look. You'll see that the bottom piece is the biggest. The 1X2 inch pieces form the sides of the bat house and then there are two smaller pieces of plywood on top. The gap between those two is a ventilation slot.

Step 2: Putting grooves on the back piece (2 hours)

This was the most difficult part of making the bat house, but it's the most important. The goal is take the plywood, which is very smooth, and roughen it up to provide places for the bat to crawl up into the house. The instructions said that you can do this by cutting grooves into the wood. Another option is to find sturdy plastic mesh and staple it along the backboard. I chose to cut grooves because I think it will look better and also if I was a bat looking for a tree, I might not be attracted to a lot of plastic. But both options apparently work.

The instructions say that the grooves need to be about a half inch apart, so I measured and marked where I thought the grooves should go.

When it came time to cut the grooves, what I found challenging was that I didn't know what type of tool to use.

Since at first I was shy about using the circular saw, I tried to use a hand saw. After 30 minutes and only three grooves, I realized I would have to rely on technology.

I set the circular saw to only 1/16 of an inch, reclamped the plywood and started cutting grooves into the backboard. They were not always perfectly straight lines, but that's not important because trees do not have perfectly straight grooves either.

Once I had cut grooves over the whole backboard with the circular saw, I took my hand saw and deepened some of the grooves. I did this because I was not sure if the circular saw went deeply enough and also to roughen it up even further.

Step 3: Staining inside the bat house (1 hour)

Bats like it dark inside their houses so it's important to stain all inside parts a dark color. First you have to sweep all the sawdust carefully from the backboard, especially from the grooves that you cut.

I chose a walnut stain because it was the darkest one at the store. It's important to use stain rather than paint because paint would fill in the grooves you just cut. Stain just soaks into the wood nicely.

It only takes two coats of the stain, and the stain dries fast if you are making your bat house outside in the sun.

Step 4: Caulking and screwing on the sides (30 minutes)

If you are going to use plastic mesh to help the bats climb inside your bat house, now is the time when you would staple it on. Make sure it hangs all the way down to the "landing pad" area so bats have something to grab on to.

Before adding the side pieces, apply caulk. This seals the bat house to help keep the heat inside. Baby bats need a warm home - reaching 80 to 100 degrees Fahrenheit in July.

Next you use your power drill to attach on the side pieces. Since these pieces are rather narrow, they can easily split. A way to avoid splitting is to pre-drill the holes with a drill bit that is smaller than the size of your screw. Then, when you drill in the screws, they go in much easier and your wood stays whole.

Step 5: Caulking and screwing on the top pieces (30 minutes)

Next, attach the top two pieces of plywood. First caulk to ensure a snug fit. Then follow the same advice for drilling and attach the larger of the two top pieces.

Before you attach the smaller of the two pieces, measure to make sure your ventilation slot is about half an inch.

Step 6: Caulking the sides and adding the roof (15 minutes)

To ensure there are no gaps between all these pieces of wood where heat could escape, leaving our poor bats shivering in the cold, put some caulk all around the sides in any gaps that you see.

Finally, add a piece of wood to the top to form a roof.

Step 7: Priming and painting the bat house (variable given paint drying time)

Finally, we need to ensure the bathouse lasts a long time so we prime and paint it. We prime it with an exterior primer that discourages the growth of any plants or mold. Here I am applying the primer. Next I painted four layers of dark paint - in my case it was dark brown.

Writer’s Note: I have to be honest with you: I built this bat house when I had little babies, and as any young mother knows, hanging a bat house doesn’t really reach the top of the “to-do” list. So I gave the bat house to a friend at the National Wildlife Federation in the hopes it might get put up here. Unfortunately we don’t know what happened to it. We looked all over, but it’s now been six years and there’s no sign of it. So, here is how you SHOULD mount your new bat house!

Step 8: Mount the Bat House (20 minutes)

Bat houses should be mounted on poles or buildings, which provide the best protection from predators. Wood or stone buildings with good solar exposure are excellent choices, and locations under the eaves often have been successful. All bat houses should be mounted at least 12 feet above ground; 15 to 20 feet is better.

I hope you enjoy building your bat house, whether it's in celebration of bats at Halloween or any time of the year. Remember, once you put up the bat house, it may take a few years for a bat to find it. They will come looking in the spring time, so ideally it should be hung by late winter.